ELECTRON TRANSPORT IN R. RUB RUM 



289 



Log C ADDITIONAL , M ;i 



Fig. 9. Effect of various substances on photoreduction of NAD by fi. rubnim 

 chromatophores. Experimental conditions were the same as for Fig. 8, except 

 that reactions were carried out at 22° C in light (approx. 900 ft-candles) in the 

 presence of 3.3 x 10-4 m nAD (56). 



normal oxidation- reduction potential ( Eq ) of bacteriochlorophyll 

 present in the cells was estimated to be 0.4-0.515 V (see also ref. 61). 

 This value might correspond to the Eq value of the nonilluminated 

 bacteriochlorophyll. Spikes et al. (62) and Vishniac (63) have demon- 

 strated that cytoplasm preparations from leaves of the wild sunflower, 

 and a mixture consisting of chlorophyll a and an aqueous- extract from 

 an acetone-dried preparation of spinach leaves, respectively, brought 

 about significant reductions in redox potential upon illumination. In 

 fact, an ethylene glycol solution of bacteriochlorophyll prepared from 

 R. rubriim showed a more negative value in light and upon cessation 

 of illumination the potential became more positive if assayed anaero- 

 bically in the presence of ascorbate with the use of platinum and 

 calomel electrodes (Fig. 11). Duysens, Huiskamp, Vos and van der 

 Hart (64) have suggested the following reactions: 



